The Synergistic Effect Of Oxides In Flame Retardant Polyolefin Cables

Polyolefins,especially linear low density polyethylene and ethylene vinyl acetate composites?LLDPE/EVA?,are widely used in wire and cable because of their excellent performance.LLDPE/EVA composite is extremely flammable and emits a lot of heat when it burns,which is harmful to human life and property safety.Therefore,it is of great significance to investigate the flame retardancy of LLDPE/EVA materials.Flame retardant LLDPE/EVA composites are fabricated by incorporating halogen-free flame retardants such as hydroxides.However,it is generally required to be used in combination with other flame retardants to achieve a better flame retardant effect due to the low efficiency of most halogen-free flame retardants.In this paper,the synergistic flame retardant effect of several oxides including molybdenum trioxide?MoO₃?and fumed silica?SiO₂?on LLDPE/EVA system was studied.The main contents are as following:?1?By blending different ratios of LLDPE and EVA,it is determined that the highest mechanical strength is achieved when the ratio of LLDPE:EVA is 80:20?mass ratio,the same below?.When the flame retardant polyolefin?PO?cable material?POMH?was prepared under the ratio of magnesium hydroxide?MH?and PO?40/60?the limit oxygen index?LOI?value was only 24.4,showing that the flame retardancy under this condition is low.When using expandable graphite?EG?as a flame retardant synergist,although the POMH-EG6?6 phr of EG to POMH?although still failed in horizontal vertical burning tests?UL-94?,the LOI value was improved to 28.2%.The synergistic flame retardant was obtained by using various oxides of?ZnO,SiO₂,Fe₂O₃,MoO₃ and SnO₂?.After adding 1 phr of MoO₃ to POMH-EG6?POMH-EG6-M2?,the LOI value was further improved to 29.5%,and also UL-94 test pass V-0.Moreover,during the mechanical tests,the elongation at break can reach 208.6%.Thermogravimetric analysis?TGA?results showed that the residual char content of POMH-EG6-M2 reached 30.47%at 800^oC,which was 20.7 times of PO.Cone calorimetry?Cone?test results showed that the peak heat release rate?PHRR?and total heat release?THR?of POMH-EG6-M2 were both reduced by 76.3%and 31.3%,respectively compared with PO,X-ray diffraction?XRD?,infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?-energy spectroscopy?EDS?and Raman spectroscopy?Raman?test results confirmed that MoO₃ at high temperatures helped the material to form a more stable carbonaceous char structure.Thermodynamic analysis showed that POMH-EG6-M2 had high activation energy in the main weight loss stage,reached 359.6 kJ/mol,indicating that the addition of MoO₃ is beneficial to improve the thermal stability of the material.?2?A cross-linked flame retardant material?XLPOMH?was prepared by using dicumyl peroxide?DCP?as a cross-linking agent and MH as a flame retardant.A small amount of oxide was added to study the synergistic flame retardant effect on the material.The LOI values of the materials was increased by 0.6%and 0.8%,respectively,after adding 1 phr of ZnO or 1 phr of SiO₂ to the crosslinked flame retardant material?XLPOMH?with a DCP addition of 0.25 phr.Cone results showed that the addition of a small amount of oxide in POMH has little effect on PHRR and THR,while adding 1 phr of SiO₂ to XLPOMH could greatly reduce the PHRR and THR by 61.78%and 60.19%,respectively.The addition of the oxides could reduce the pore number in the carbon residue of the cross-linking system.XRD and FTIR confirm that the oxide is beneficial to the material to form a more stable char layer.